There are several applications requiring an efficient source of energy which must be self-contained due to the unavailability of elemental fuel inputs such as oxygen and the combustible material. Such applications are typically in remote areas as for example in undersea or space environments where the additional requirement of high energy density, that is high kw output per pound of heat system, is an important design objective. In addition, certain applications such as in undersea motors, require that no exhaust product be given out by the energy system. Finally, some applications further require the ability to control the level of power output in response to system energy demands and the ability to conserve fuel during periods of low or no energy need. At the same time, system efficiency should be maintained high at all levels of controlled output including very high energy, or "burst" energy output modes.
Among available energy sources, the fuel cell is typically employed in remote regions requiring controlled energy sources usable over substantial periods of time. As measured in terms of energy density, the fuel cell provides a relatively low energy output per pound of energy supply system and is thus inefficient for use in many remote applications.